“The mountain got too steep for him,” said Clark campaign spokesman Matt Bennett. The “tremendous momentum” that Sen. John Kerry gained from early primary victories in Iowa and New Hampshire were too great to overcome, he said

Mr. Clark will make a personal speech of gratitude to staffers in Little Rock, Ark., before formally announcing his departure from the race at 2 p.m. CST at the Peabody Hotel.

Mr. Bennett said the retired four-star Army general has not decided on any endorsements, but will pledge to work closely with the Democratic Party.

“He made this decision after discussing it with his family and his staff,” Mr. Bennett said. “It was a very difficult decision to make, obviously. He did it after the final results were in for Tennessee and the decision is final.”

In a speech to supporters in Memphis before the Tennessee results were final last night, Mr. Clark did not talk about his future.

“We may have lost this battle today, but I will tell you what: We are not going to lose the battle for America’s future,” said Mr. Clark, who had considered pulling out before his lone victory in Oklahoma last week.

Both Mr. Clark, an Arkansan, and North Carolina Sen. John Edwards, who finished second to Mr. Kerry in both of yesterday’s primaries, had predicted their Southern roots would pay off and make them the last remaining challenger to Mr. Kerry of Massachusetts.

“Both Edwards and Clark banked on Southern states, and now I’d like to see them get unified,” said Randy Button, chairman of the Tennessee Democratic Party. “Clark got in late, but he started campaigning here quickly and was the first to go up on TV.”

Mr. Clark finished a distant third in Virginia, garnering just 9 percent of the vote, 18 points behind Mr. Edwards and more than 40 points behind Mr. Kerry.

Mr. Clark fared better in Tennessee, finishing fewer than five percentage points behind Mr. Edwards’ second-place showing. Mr. Kerry dominated both contests yesterday, making him the victor in 12 of the 14 contests held so far.

Mr. Edwards vowed to fight on, saying the race to challenge President Bush was now down to him and Mr. Kerry.

“It looks like it’s narrowed itself down to a two-person race now, and we’re excited about our prospects,” Mr. Edwards said on CNN. “He’s in front and I’m the underdog, and I’m fighting.”

One senior Democratic Party official, speaking on the condition of anonymity, suggested party leaders would let the race play out at least until next week’s Wisconsin primary before coming down hard on the also-rans.

New to politics, Mr. Clark may still have a future. At 59, he is young enough for another race and, with his military experience, he might fit on a wartime Democratic ticket.

Mr. Clark entered the race in September, a late start for a neophyte campaigner, but he quickly rose to the top of polls of Democrats and others considering an alternative to President Bush. He decided to skip the Iowa caucuses to focus all of his efforts on New Hampshire, a move that some friends and family now call a mistake.

In appealing to voters, Mr. Clark relied almost entirely on his 34 years in military service, which included serving as supreme allied commander of NATO. He promoted his wartime record, from being wounded in Vietnam in 1970 to running the bombing campaign in the war in Kosovo in 1999, as the kind of experience needed with American soldiers in Iraq and concerns about security at home.

One-time front-runner Howard Dean abandoned yesterday’s Southern contests to focus on Wisconsin, where he is currently polling in the single digits. The former Vermont governor has not won a contest and is nearly out of money, but has vowed to continue the fight past next Tuesday’s contest.

Ohio Rep. Dennis J. Kucinich and the Rev. Al Sharpton have remained in the contest despite being winless — and have indicated that they intend to push on, regardless of how well they do in upcoming primaries.

Maya Alleruzzo contributed to this article, which is based in part on wire service reports.